This invention relates generally to single-phase, three-wire power distribution systems, and, more particularly, to systems of this kind having means for detecting an improper polarity in the power signals carried on the three wires.
Power distribution systems of this general type are commonly used at construction sites to supply power to portable tools and the like. These systems ordinarily receive single-phase power on a three-wire line, which carries a positive power signal, a neutral power signal and a negative power signal, with the positive and negative power signals having opposite polarities. The system includes a number of standard ground fault interrupters and associated outlet connectors for providing protected output power.
Occasionally, the three-wire line supplying power to the system can be accidentally severed. When this occurs, personnel at the site will ordinarily attempt to reconnect the line, but a hazard can arise if they fail to correctly match up the severed wires. For example, if the wires ordinarily carrying the positive power signal and neutral power signal are reversed, some of the system's outlet connectors will supply double voltage levels.
It should therefore be appreciated that there is a need for a power distribution system having means for sensing such an incorrect polarity in a single-phase, three-wire power input line, and for uncoupling power from a number of outlet connectors when that occurs. The present invention provides a simple, low-cost and extremely reliable solution to that need.